<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
        width: 200px;
        height: 200px;
    }

    /* margin合并了 会选择最大的像素 */
    .div1 {
        margin-bottom: 80px;
        color: black;
    }

    .div1 {
        color: brown;
        margin-top: 20px;
    }
    </style>
</head>
<body>
    <div class="div1">
        div1
    </div>

    <div class="div2">
        div2
    </div>


    <!-- 父子级标签塌陷问题 -->
</body>
</html>